In tire manufacturing, high cis 1,4-polybutadiene (e.g., rubber with a cis 1,4 linkage content of 95% or greater) is a rubber commonly used for its excellent mechanical properties. Nickel-based catalysts are generally utilized in the synthesis of high cis 1,4-polybutadiene rubbers. Nickel-based catalysts comprise a nickel compound, an organoaluminum compound, and a halogen compound. Nickel-based catalysts have utilized boron based halogen compounds, such as BF3, with an organic solvent; however, conventional polymerization processes remove all water from the solvent, because of concerns that water will hydrolyze the BF3, thereby degrading BF3 and producing undesirable byproducts such as boric acid and fluoroboric acid. Other polymerization processes have utilized some amount of water; however, the water is not incorporated in the BF3 component of the catalyst in these polymerization processes.
Accordingly, a continual need exists for improved catalyst systems which utilize water in the boron component of the catalyst to increase the polymerization rate while regulating the molecular weight or Mooney viscosity of the 1,4-polybutadiene.